Current supply apparatus for load voltage regulation



Sept. 2, 1958 J. D. BISHOP 2,350,695 1 CURRENT SUPPLY APPARATUS FOR LOADVOLTAGE REGULATION Filed Aug. 5. 1955 ATTORNEY ..decrease. .curre nt, anincrease of load current will result in a subfload voltage,substantially constant. vrent has-.aminimum value .whi'chmay be nearlyzero,

United States qCURRENT SUPPLY APPARATUS F022 LGAH) VOLTAGE REGULATIONJohn D. Bishop, Summit, N. 3., assignor to Bell Teie= phoneLaboratories, Incorporated, New York, N. Y, acorporation of New YorkApplication August 3, 1955,5erial No. 526,306

8 Claims. ((1323-22) Thisinvention relates to current supply apparatusand moreparticularly to apparatus for controlling the supply of currentfrom a current source to a load to minimize changes 1 of load voltage.

An object of the invention is to provide an improved current supplycircuit including a transistor or transistors to set up across a loada'substantially constant voltage havinga desired magnitude.

Another object of the invention is to provide a current supply circuitcomprising one or more transistors for maintaining a substantiallyconstant load voltage over a predetermined range of load current andover a wide range of ambient temperatures.

This invention is animprovement over the invention disclosed and claimedin an application of B. H. Hamilton, Serial No. 441,871, filed July 7,1954.

In a specific embodiment of the invention herein shown and described forthe purpose of illustration, direct current is supplied from a rectifierthrough a series resistor to a load circuit. A shunt current pathconnected across the load comprises the emitter and collector of a firsttransistor which may be of the p-n-p, for example.

There, is provided a transistor detector-amplifier comprising asecondand a third transistor responsive to load voltage changes forcontrolling the base current of the jfirst transistor and thereby thecurrent flowing in the .shunt.current path across the load. .thirdtransistors may beof the p-n-p and n-p-n types,

The second and respectively, for. example. There are provided a currentpath-connecting the base of the first transistor and the emitter of thesecond transistor and a current path con- .necting the base of thesecond transistor and the collector of thethird transistor. Current issupplied from the rectifier through a first resistive path into theemitter and out. of the collector of the second transistor. 313150supplied from the rectifier through a'second resistive path into thecollector and out of the emitter of the Current is third transistor. Acircuit connecting the base and ,ernitterof the third transistorcomprises a source of voltage-proportional to the load voltage and, inopposition thereto, asource of substantially constant reference voltage.

A decrease of load voltage due to an increase of load current,forexample, Will makethe potential of the .baseof the. third transistorrelatively less positive or more negativewith respect to its emitterpotential. As a result, the currents flowing into the collector of thethird tran- .sistor, into. the emitter of the second. transistor andinto theemitter :of the first transistor, respectively, will each Inthis way, over an operating range of load .stantially equal decrease ofcurrent flowing into the emitterof the first transistor, therebymaintaining the When theload curr 2,850,693 Fatented Sept. 2, 1958 icemined by the minimum current flowing into the emitter of the firsttransistor. A maximum operating range of load current at substantiallyconstant load voltage is thus obtained if the current flowing into theemitter of the first transistor can be reduced substantially to Zero.Any increase of load current beyond a value which causes the emittercurrent of the first transistor to be reduced to a minimum emittercurrent will result in a decrease of load voltage.

At a relatively low ambient temperature, 20 degrees centrigrade, forexample, a reduction of the current flowing out of the base of the'firsttransistor substantiallyto zero causes the current flowing into itsemitter and out of its collector to be reduced nearly to zero.- However,an increase of ambient temperature to 60 degrees centigrade, forexample, with the base current at zero, will result in a substantiallyhigher current flowing into the emitter and out of the collector. Withthebase current at zero, this increase of ambient temperature would thusresult in a considerable decrease of the load current at substantiallyconstant load voltage. To permit the emitter current of the firsttransistor to be reduced substantially to zero at a relatively highambient temperature, there is provided a resistive current path forconnecting the base of the first transistor and the emitter of thesecond transistor to the positive terminal of the rectifier. With thisarrangement the base current of the first transistor will reverse, wthenthe emitter current of the second transistor is reduced sufficiently,that is, current will flow through the resistive current path into thebase of the transistor. There is also provided a resistive current pathconnecting the base of the second transistor and the collector of thethird transistor to the positive rectifier terminal so that, when thecollector current of the third transistor is reduced sufficiently,current may flow through the resistive current path into the base of thesecond transistor, thereby further reducing the emitter current of thesecond transistor. For operating conditions which may be considered tobe normal, load voltage changes are minimized over a Wide range of loadcurrent including a certain maximum load current and over a widerange-of ambient temperature.

An asymmetrically conducting diode is provided in a path connecting thebase of the second transistor to the positive load terminal to preventthe bases of the first and second transistors and the collector of thethird transistor from rising to a potential considerably higher than thepotential of the positive load terminal. The circuit is designed sothat, without the diode'in'the circuit, these potentials would notbecome excessive as long as the regulating circuit i capable ofmaintaining the load voltage substantially constant. For this condition,the base of each of the first and second transistors may rise to apotential of a few tenths of a volt positive with respect to the emitterpotential, for example, with the result that the current flowing intothe'base is substantially equal to the current flowing out of thecollector. However, if the load voltage should decrease substantiallybelow the normal constant voltage due tothe battery across the loadbecoming discharged, the collector current of the first transistor maybe reduced to zero, for example. If the diode were not provided, thiswould result in the voltage between the emitter and collector electrodesof the third transistor and the voltage between the'base-and collectorelectrodes of the first and second transistors rising to a magnitudesuch that the maximum voltageand dissipation ratings of the transistorswould be exceeded. By connecting the base-ofthe secondtransistor'through an asymmetrically conducting diodeto the positiveload terminal, each of the three transistors is restricted to operatingwithin the normal voltage; and collector-dissipation 32 of 215 ohms.

) 3 ratings with the result that damage to the transistors is avoided.

The invention will now be described in greater detail with reference tothe accompanying drawing the single figure of which is a schematic viewof a current supply apparatus embodying the invention.

Referring now to the drawing, there is provided a transformer having aprimary winding connected to a 1l5-volt, oil-cycle per second,alternating-current supply source 11 and having a secondary winding 12shun by a condenser 13 of 2400 micro-mlcrofarads, for ex. 1 ple. Thetransformer winding 12 is connected to the in put terminals of a bridgerectifier 14. The positive output terminal of the rectifier 14 isconnected through a series resistor 15 of 127 ohms, for example, to thepositive terminal 16 of a load circuit comprising a dissi ative load 18which may vary and a floating battery 19 c 1 nected across the load. Thenegative terminal 11' of the load is connected through an asymmetricallyconducting varistor or diode and a resistor 41 having a resistance of0.422 ohm, for example, in series, to the negative terminal of rectifier14. A condenser 42 of 101 microfarads is connected across the outputterminals of rectifier 14. A transistor regulating circuit is providedfor maintaining the load voltage substantiaily constant at 22 volts, forexample, for a range of load current up to and including a predeterminedmaximum value, 0.1 ampere, for example.

The regulator comprises a first transistor 20 of the pnp type, a secondtransistor 21 of the pnp type and a third transistor 22 of the npn type,each transistor having a collector, an emitter and a base. The emitterof transistor 20 is directly, conductively connected to the positiveload terminal 16 and the collector of transistor 253 is connectedthrough a resistor 26 of 81.6 ohms, for example, to the negative outputterminal of rectifier 14. The base of transistor 20 is directly,conductively connected to the emitter of transistor 21. The base oftransistor 20 and the emitter of transistor 21 are connected through aresistor 23 of 8250 ohms, for example, to the positive output terminalof rectifier 14. A voltage divider comprising a resistor 43 of 121 ohmsand a resistor 2'7 of 562 ohms, in series, is connected between thepositive load terminal 16 and the negative terminal of rectifier 14. Thecollector of transistor 21 is connected to the common terminal ofresistors 43 and 27.

The collector of transistor 22 is connected through a resistor 28 of2150 ohms, shunted by a condenser 44 of 2400 micro-microfarads, and aresistor 29 of 8250 ohms, in series, to the positive output terminal ofrectifier 14. The base of transistor 21 is connected to the commonterminal of resistors 28 and 29 and this common terminal is connectedthrough an asymmetrically conducting varistor or diode to the positiveload terminal 16. There is provided a p-n junction diode 33 to whichcurrent is supplied through a circuit which may be traced from thepositive output terminal of rectifier 14, through resistor 15 andthrough a resistor 46 of 3160 ohms to one terminal of diode 33, and fromits other terminal, through resistor 41 to the negative output terminalof rectifier 14. The emitter of transistor 22 is connected to the commonterminal of resistor 46 and the constant voltage diode 33. There is thussupplied through the diode 33 in its reverse or high resistancedirection, current of suflicient amplitude to cause a substantiallyconstant unidirectional reference voltage to be set up across the diode.A condenser 47 is provided in a path connecting the col lector and baseof transistor 22.

There is connected between the positive load terminal 16 and thenegative terminal of rectifier 14 a section voltage dividing pathcomprising in series a resistor 30 of 750 ohms, a potentiometer 31 of196 ohms and a resistor The base of transistor 22 is connected to thevariable tap of potentiometer 31. The constant reference voltage acrossthe diode 33 is in opposition to the voltage across resistor 32 and aportion of potentiometer 31 in the circuit connecting the base andemitter of transistor 22. The diode 46 is provided to prevent dischargeor" the battery 19 through the regulator circuit if thealternating-current supply source 11 should fail. The resistor 41 isconnected in the base-emitter circuit of transistor 22 so as tocompensate for the voltage drop produced by the load current flowingthrough the diode 41 When the load current does not exceed the upperlimit of a normal operating range, 0.1 ampere, for example, theregulating circuit will main the load voltage substantially constant at22 volts, for example, over a wide range of ambient temperature, sayfrom minus 40 degrees Fahrenheit to plus 14-0 degrees Fahrenheit. If theload current should increase, for example, the voltage drop acrossresistor 15 would increase to cause a reduction of the load voltage. Thereduction of load voltage makes the base of transistor 22 relativelyless positive with respect to the emitter of transistor 22. The currentflowing through resistors 29 and 28 into the collector of transistor 22is thus reduced and the base of transistor 21 becomes relatively lessnegative or even slightly positive with respect to the emitter oftransistor 21. As a result, the current flowing through resistor 23 intothe emitter and the current flowing out of the collector of transistor21 are reduced and the potential of the base of transistor 20 becomesless negative or even slightly positive with respect to the emitter oftransistor 20. Therefore, the current flowing into the emitter and thecurrent flowing out of the collector of transistor 20 are reduced. Inthis way, as the load current increases, the current flowing in theshunt path comprising transistor 20 and resistor 26, in series,decreases, thereby minimizing changes of current flowing throughresistor 15 and changes of load voltage.

The regulator also corrects for changes of output voltage of rectifier14 due to voltage changes of the supply source 11 in a somewhat similarmanner. A decrease of 'output voltage of rectifier 14, for example,causes both the load voltage and the voltage across resistor 15 to bereduced. The regulator then functions to reduce the current flowing inthe shunt current path comprising transistor 20 to cause a furtherreduction of the voltage drop across resistor 15. This reduction ofvoltage across resistor 15 minimizes the voltage change across the load.

The voltage drop across resistor 41 increases in response to an increaseof load current and the voltage across the diode 40 also increasessomewhat in response to an increase of load current. The voltage acrossresistor 41 is included in the base-emitter circuit of transistor 22 tocompensate for the change in voltage drop across the diode 40 When theload current changes. An increase of voltage drop across the diode 40due to an increase of load current, for example, would reduce the loadvoltage if no compensation for this effect were provided. However, theaccompanying increase of voltage drop across resistor 41 due to theincreased load current makes the base of transistor 22 relatively lesspositive with respect to the emitter potential. As a result the emittercurrent of transistor 21) is decreased to cause the voltage drop acrossresistor 15 to decrease, thereby compensating for the increased voltagedrop across the diode 40.

It is desirable to maintain the load voltage constant over a wide rangeof load current. A maximum operating range of load current is realizedwhen the current flowing into the emitter of transistor 20 can bereduced to zero. At a relatively low ambient temperature, a reduction ofthe current flowing out of the base of transistor 20 to zero will causethe current flowing into the emitter and out of the collector to bereduced nearly to zero. However, the minimum or leakage collectorcurrent of the transistor increases with increasing ambient temperature.At a relatively high ambient temperature, therefore, in order to reducethe emitter curent substantially to Zero, it is necessary for the basecurrent to reverse so that the current flowing into .the base issubstantially equal to the current flowing out of the collector.

Let us first consider the operation of the circuit with the diode orvaristor 45 omitted and with the ambient temperature relatively high.Assume further that the load current increases to a maximum amplitudewithin the normal operating range for constant load voltage, or nearlyso. The resulting decrease of load voltage will cause the curent flowingthrough resistor 29 into the collector of transistor 22 to be reduced toincrease the potential of the base of transistor 21. The current flowingout of the base is reduced or, possibly, the potential of the base maybecome slightly positive with respect to the emitter so that curentflows into the base and out of the collector of transistor 21. Theresulting reduction of current flowing through resistor 23 into theemitter of transistor 21 causes the potential of the emitter oftransistor 21 and the potential of the base of transistor 20 toincrease. The base potential of transistor 20 be comes positive withrespect to its emitter potential by a few tenths of a volt and thecurrent flowing into the base is substantially equal to the currentflowing out of the collector. The emitter curent of transistor .20 isthus reduced substantially to zero.

If the load current should further increase by a substantial amount, dueto battery 19 becoming discharged, the increased voltage drop acrossresistor 15 will be sufficiently'large to reduce the load voltageconsiderably below its normal, substantially constant amplitude. As aresult of the reduction of load voltage, the current flowing throughresistor 2% into the collector of transistor 22 may be reduced to zero,for example. The potential of the base of transistor 21 may thereforerise to an abnormally high value, say, to the potential of the positiveterminal of rectiflerl. If, under the normal condition of substantiallyconstant load voltage, current flowsthrough resistor 23 into the emitterand out of the base of transistor 21, through resistor 28 and into thecollector of transistor 22, this current is interrupted for theabnormally low load voltage condition, so that the potential of the baseof transistor 20 also rises to an abnormally high value, that is, to thepotential of the positive terminal of rectifier 14. Without the use ofthe diode 45, therefore, the base to collector voltages of transistors20 and 21 and the collector to emitter voltage of transistor 22 mayincrease to such amplitudes, under an abnormal operating condition, asto cause the transistors to become damaged by exceeding the safeoperating limits.

The use of the diode 45 prevents damage to the transistors by limitingthe potential increase of the bases of transistors 20 and 21 and of thecollector of transistor 22. Whenever the potential of the base oftransistor 21 and of the collector of transistor 22 becomes positivewith respect to the potential of the positive load terminal 16, currentflows from the positive output terminal of rectifier 14 through resistor29 and through the diode 45 to the positive load terminal. The resultingincreased voltage drop across resistor 29 prevents the base oftransistor 21 and the collector of transistor 22 from increasing morethan a few tenths of a volt above the potential of the positive loadterminal. When the potential of the base of transistor 21 rises to anexcessively high value, the emitter of transistor 21 and, therefore, thebase of transistor 20, also rises to an excessively high potential, thebase and emitter of transistor 21 being nearly at the same potential.Thus, preventing an increase of potential of the base of transistor 21to an excessively high value also prevents the base of transistor 20from risiri to an excessively high potential.

The use of the voltage divider comprising resistors 43 and 27 increasesthe potential of the collector of transister 21 with respect to thepotential of the negative output terminal of rectifier 14. Thisarrangement reduces the emitter-collector voltage of transistor 21 andpermits a higher output current of transistor 21 while preventing excessdissipation therein.

What is claimed is:

l. in combination, a transistor having a plurality of electrodescomprising an emitter, a collector and'a 'base, means for supplyingunidirectional current from a directcurrent supply source into oneofsaid emitter and collector electrodes and out of the other of saidemitter and collector electrodes, a resistive current path connectingsaid base to said current supply source,'means for supplying varyingunidirectional current from said source to said resistive path tocontrol the potential of said base with respect to the potential of'saidemitter and means for limiting the voltage of a predetermined polaritybetween said emitter and said base comprising means for furthercontrolling the current through said resistive path.

2. In combination, a transistor having 'a plurality or electrodescomprising an emitter, a collector and a base, a source ofdirect-voltage, a resistor, a first direct current circuit comprising inseries said resistor, said emitter and collector electrodes and saidvoltagesource, means for varying the current in said first'circuit,an'asymmetrically conducting varistor and a second direct-currentcircuit comprising in series said voltage source, said resistor and saidvaristor in which circuit current is caused to flow in response to areduction toa predetermined amplitude of the current flowing in the saidfirst circuit.

3. An "electric circuit comprising an n-p-n transistor havingacollector, an emitter and a base, a source of direct voltage havingpositive and negative'terminals, a resistor having a first "and a secondterminal, means 'for connecting the first terminal of said resistor tosaidipositive terminahmeans for 'connectingthe second terminal of saidresistor to said collector, a current path connecting said emitter tosaid negative terminal, means for controlling the potential of said'baseto'vary the current flowing through said resistor into said collector,an asymmetrically conducting varistor and a currentpath comprising saidvaristor for connecting the second terminal of said resistor to a pointin said circuit having a lower potential than the potential of saidpositive terminal.

4. An electric circuit comprising a transistor having a collector, anemitter and a base, a source of direct voltage having a positive and anegative terminal, means for connecting said emitter to one of saidterminals, means for connecting said collector to the other of saidterminals, an asymmetrically conducting varistor and means forcontrolling the potential of said base comprising a resistive pathconnecting said base to said positive terminal, means for varying thecurrent supplied from said source to said resistive path and a pathincluding said varistor connecting said base to a point in said circuithaving a lower potential than the potential of said positive terminal.

5. An electric circuit comprising a transistor having a collector, anemitter and a base, a source of direct voltage having a positive and anegative terminal, means for connecting said collector to one of saidterminals, a first and a second resistor, means for connecting saidemitter through said first resistor to the other of said terminals,means for connecting said base through said second resistor to saidother terminal, a circuit for supplying to said second resistor fromsaid supply source a current which may vary, an asymmetricallyconducting varistor and means for connecting said base through saidvaristor to a point in said circuit having a potential intermediate thepotentials of said positive and negative terminals.

6. An electric circuit comprising a first and a second transistor eachhaving a plurality of electrodes comprising a collector, an emitter anda base, a direct voltage source having a positive and a negativeterminal, current paths for connecting one of said collector and emitterelectrodes of said transistors, respectively, to said negaa currentwhich may vary, an asymmetrically conducting varistor and means forconnecting said base of said second transistor through said varistor toa point in said circuit of lower potential than the potential of saidpositive terminal.

7. Appraratus for supplying current from a direct-current supply sourcehaving a posititive and a negative terminal to a load circuit includinga load having a positive and a negative terminal comprising a firstresistor for connecting the positive terminal of said source to thepositive terminal of said load, means for connecting the negativeterminal of said source to the negative terminal of said load, a firsttransistor of the p-n-p type having a first collector, a first emitterand a first base, means for connecting said first emitter to saidpositive load terminal, means for connecting said first collector tosaid negative terminal of said source, a second transistor of the p-n-ptype having a second collector, a second emitter and a second base,means for conductively connecting said first base to said secondemitter, a second resistor for connecting said first base and saidsecond emitter to said positive terminal of said source, a thirdresistor for connecting said second base to said positive terminal ofsaid source, a voltage divider comprising a fourth and a fifth resistorin series connecting said positive load terminal to the negativeterminal of said source, means for connecting said second collector tothe common terminal of said fourth and fifth resistors, anasymmetrically conducting varistor connecting said second base to saidpositive load terminal, said varistor being poled to conduct currentthrough it in the low resistance direction from said second base to saidpositive load terminal, a third transistor of the n-p-n type having athird collector, a third emitter and a third base, a current pathcomprising said third resistor for connecting said third collector tosaid positive terminal of said source and means for impressing upon saidthird base with respect to said third emitter a potential havingvariations corresponding to load voltage changes.

8. In a circuit for supplying current from a directcurrent supply to aload circuit comprising a dissipative load and a floating battery acrossacross said dissipative load, regulating means, means for controllingsaid regulating means in response to load voltage changes for minimizingvoltage changes across said load, means for normally supplyingenergizing current from said supply source to said regulating means, anasymmetrically conducting varistor, means for connecting said varistorin series with said load circuit and said regulating means to minimizethe discharge of said battery through said regulating means in the eventof failure of said supply source under an abnormal condition, thebattery discharge current through said regulating means flowing throughsaid varistor in its reverse or high resistance direction, said varistoralso being connected in series with said supply source and said loadcircuit so that the load current normally flows through said varistor inits forward or low resistance direction to produce a voltage drop acrosssaid varistor which increases in response to an increase of loadcurrent, and means for further controlling said regulating means toreduce or substantially prevent a change of load voltage due to a changeof voltage drop across said varistor.

References (lited in the file of this patent UNITED STATES PATENTS2,316,331 Hedding Apr. 13, 1943 2,693,568 Chase Nov. 2, 1954 2,693,572Chase Nov. 2, 1954 2,714,702 Shockley Aug. 2, 1955 2,747,111 Koch May22, 1956

